Project Summary/Abstract The rare disease dyskeratosis congenita (DC) is caused by genetic deficiencies in the maintenance of telomeres, which are the structures that protect the ends of chromosomes. Premature telomere shortening leads to widespread organ pathology, including bone marrow failure, fibrotic scarring of the lungs (pulmonary fibrosis) and liver (hepatic cirrhosis), and gastrointestinal disorders. Bone marrow transplantation can successfully address marrow failure, but other pathologies are not treated effectively. In studies funded by an NIH R21 grant, the principal investigators demonstrated recently that intestinal pathology involves loss of normal support of stem cell function by an intercellular communication pathway called Wnt, and that drugs that restore Wnt pathway signaling (including lithium) can ameliorate this pathology. Here we propose to investigate lung and liver pathology, in particular to determine if Wnt activators are beneficial in these tissues as was observed in the intestine. We will also broadly investigate other affected pathways that might provide points of therapeutic intervention. We will use human induced pluripotent stem cells (iPSCs) and genome editing to generate key lung and liver cells that can be studied in culture, along with telomerase deficient mouse models, to investigate these mechanisms and test new therapeutic approaches focused on using existing FDA-approved drugs. The specific aims are: 1. Characterize defects in human DC iPSC-derived cultured type II alveolar epithelial stem cells, and test the capacity of pharmacologic manipulations aimed reversing the altered pathways to ameliorate these defects. 2. Characterize defects in human DC iPSC-derived cultured hepatocytes and stellate cells, and test the capacity of pharmacologic manipulations aimed at reversing the altered pathways to ameliorate these defects. 3. Use mouse models to address the efficacy of pharmacologic manipulations to rescue human DC mutant iPSC-derived tissues in an in vivo context. This will include determination of the minimum serum lithium concentration that will rescue human tissues transplanted into mice, and tests of lithium and other small molecules to rescue mouse models of pulmonary fibrosis and cirrhosis driven by telomere dysfunction.